With remarkable development of information technology (IT), a great variety of portable information communication devices has been popularized. As a result, in the 21st century, we are moving toward a ubiquitous society in which high-quality information service is possible regardless of time and place.
Lithium secondary batteries are very important to realize such a ubiquitous society. Specifically, lithium secondary batteries, which can be charged and discharged, have been widely used as an energy source for wireless mobile devices. In addition, the lithium secondary batteries have also been used as an energy source for electric vehicles and hybrid electric vehicles, which have been proposed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
As devices, to which the lithium secondary batteries are applicable, are diversified as described above, the lithium secondary batteries have also been diversified such that the lithium secondary batteries can provide powers and capacities suitable for devices to which the lithium secondary batteries are applied. In addition, there is a strong need to reduce the size and weight of the lithium secondary batteries.
Small-sized mobile devices, such as mobile phones, personal digital assistants (PDAs), digital cameras, and laptop computers, use one or several small-sized, lightweight battery cells for each device according to the reduction in size and weight of the corresponding products.
On the other hand, middle or large-sized devices, such as electric bicycles, electric motorcycles, electric vehicles, and hybrid electric vehicles, use a middle or large-sized battery module (middle or large-sized battery pack) having a plurality of battery cells electrically connected with each other because high power and large capacity are necessary for the middle or large-sized devices.
A cylindrical battery, a prismatic battery, and a pouch-shaped battery, which are classified based on their shapes, are used as a unit cell of a battery module or battery pack. Among these batteries, the pouch-shaped battery, which can be stacked with high integration, has a high energy density per unit weight, is inexpensive, and can be easily modified, has attracted considerable attention.
FIGS. 1A and 1B are exploded perspective views typically showing the general structure of a conventional representative pouch-shaped battery.
Referring to FIG. 1A, a pouch-shaped battery 10 includes a stacked type electrode assembly 20 configured to have a structure in which a plurality of cathodes cut into a predetermined size and a plurality of anodes cut into a predetermined size are sequentially stacked in a state in which a plurality of separators cut into a predetermined size is disposed respectively between the cathodes and the anodes, the stacked type electrode assembly 20 having pluralities of electrode tabs 21 and 22 protruding therefrom, two electrode leads 30 and 31 respectively connected to the electrode tabs 21 and 22, and a battery case 40 to receive the stacked type electrode assembly 20 in a sealed state such that portions of the electrode leads 30 and 31 are exposed outward from the battery case 40.
The battery case 40 includes a lower case 42 having, a depressed receiving part 41, in which the stacked type electrode assembly 20 is located, and an upper case 43 to cover the lower case 42 such that the stacked type electrode assembly 20 is sealed in the battery case 40. The upper case 43 and the lower case 42 are connected to each other by thermal welding in a state in which the stacked type electrode assembly 20 is mounted therein to form an upper end sealed part 44, side sealed parts 45 and 46, and a lower end sealed part 47.
As shown in FIG. 1A, the upper case 43 and the lower case 42 may be configured as separate members. As shown in FIG. 1B, on the other hand, one end of the upper case 43 may be integrally formed at a corresponding end of the lower case 42 such that the upper case 43 and the lower case 42 may be hingedly connected to each other.
Also, as shown in FIGS. 1A and 1B, the pouch-shaped battery is configured to have a structure in which electrode terminals constituted by the electrode tabs and the electrode leads connected to the electrode tabs are formed at one end of the stacked type electrode assembly. Alternatively, a pouch-shaped battery configured to have a structure in which electrode terminals are formed at one end and the other end, opposite to one end, of an electrode assembly may also be manufactured using the above method.
Meanwhile, FIGS. 1A and 1B show the stacked type electrode assembly. Alternatively, the pouch-shaped secondary battery of FIGS. 1A and 1B may be manufactured using a jelly-roll type (wound type) electrode assembly configured to have a structure in which a long sheet type cathode and a long sheet type anode are wound in a state in which a long sheet type separator is disposed between the cathode and the anode or a stacked and folded type electrode assembly configured to have a structure in which a plurality of stacked type electrode assemblies is folded in a state in which a long sheet type separation film is disposed between the respective stacked type electrode assemblies.